Magnesium alloy



Patented June 18, 1940 MAGNESIUM ALLOY Arthur Burkhardt,Berlin-Lichterfelde, and Richard Knabe, Berlin-Zehlendorf, Germany,assignors to Georg Von Giesches Erben,

Breslau, Germany, a No Drawing.

corporation of Germany Application September 3, 1938,

Serial No. 228,323. In Germany September 21,

3 Claims.

Our invention relates to magnesium alloys, and more particularly toalloys of the class containing aluminium and bismuth.

It is an object of our invention to improve a magnesium alloy of theclass aforesaid, with a view to increasing its strength, withoutdeteriorating its resistance to corrosion.

Magnesium alloys as known heretofore and having satisfactory resistanceto corrosion, are not strong, their strength being not much in excess of30 kilogrammes per square millimeter. It is true that the strength canbe increased to about 38 kgnlsq. mm. by suitable heat treatment but thisis at the expense of corrosion resistance; ,The corrosion resistance ofmagnesium alloys is poor per se, and by the segregations which occurduring the heat treatment, it is deteriorated to such an extent that therange of usefulness of such comparatively strong alloys is very'limited.Nor does the addition of manganese-which generally increases theresistance to corrosion-exert any favorable influence in the case of thealloys in consideration.

However, it has been found that the resistance to corrosion is notdeteriorated if strength-increasing alloying elements are added in suchquantities that such elements prevent the formation of a second phase.In the single-phase alloys thus produced the heterogenous inclusionswhich act as local elements and are the cause of poor corrosionresistance insecond-phase alloys of high strength, are absent. When sucha single-phase alloy is heat treated for increasing its strength,segregation does not occur at the grain boundaries but, in uniformdistribution, within the crystals themselves, so that the corresionresistance is not deteriorated.

Starting with these considerations, we have made the surprisingdiscovery that magnesium alloys of the class referred to in which thecontent of aluminium is 8 to 14%, and the content of bismuth is 2 to 4%,possess very high strength in heat treated condition.

The remainder of the alloys may be substantially allmagne'sium. Thephrase substantially all magnesium is intended to include magnesium andmagnesium with the usual impurities in technical magnesium, and minoramounts of alloying elements, provided that the said constituents arepresent only in such percentages as not to overstep the limit of solidsolubility in the mixed crystal. ents are 0.1 to 1%.

The usual rates of such constitu- The usual alloying elements are, forinstance, calcium which is added for improving the castability of thealloys; manganese for increasing their resistance to corrosion; or'atleast one metal of the iron group, or silicon, for improving thestrength of the alloys under high temperature conditions, and forincreasing their yield point.

Examples of suitable alloys-according to our invention will appear fromthe following table.

Alloy No. 132 1? gfi gg" he a t ii e t ed, Elfigga percent p c kg/sq.mm. percent It is understood that in all cases the remainder issubstantially all magnesium.

The alloys Nos. 2 and 3 are particularly good.

We claim:

nesium.

3. A magnesium alloy containing from 8 to 14 per cent aluminium, 2.5 to4 per cent bismuth, the remainder substantially all magnesium.

ARTHUR BURKHARDT. RICHARD KNABE.

